The invention relates to fluid dispensing apparatus and more particularly to a programmable volume dispensing apparatus.
Piston pumping or positive displacement dispensing provides an ideal method for dispensing certain heavy (high solids, high viscosity) fluids. Precise and repeatable volumes can be dispensed by setting the distance a pump piston travels. A solder paste dispenser for discretely controlled deposition of very small quantities of a viscous fluid at each of a succession of locations on surface mounted device boards is described in U.S. Pat. No. 4,572,103 issued Feb. 25, 1986 to Harold J. Engel. However, if different volumes of dispensing fluids are desired for a series of dispensed fluid shot, the dispensing apparatus must be stopped and manually adjusted to an appropriate setting for the shot volume desired. A trial and error sequence is used to obtain a specific shot volume which involves using precision optical equipment and/or weight measurement of each dispensed shot using specialized instruments. Where many different shot volumes of soldering paste are required for soldering varying sizes of surface mounted devices on a printed wiring board, such a trial and error process must be repeated many times which is not practical for a reliable, cost effective, production line operation.
The manner in which the invention overcomes the disadvantages of the prior art by providing a novel dispensing apparatus for varying the volume of fluid dispensed under programmable control will be understood as this specification proceeds.